Energy Prepayment Agreement (Details) - USD ($) $ in Billions	3 Months Ended	9 Months Ended
Jun. 30, 2018	Jun. 30, 2019
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Proceeds from Maturities, Prepayments and Calls of Other Investments	$ 0.0	$ 1.5

The cash inflow associated with the maturity (principal being due), prepayment and call (request of early payment) of other investments not otherwise defined in the taxonomy.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585

Name:	us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfOtherInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration